Copending U.S. patent application Ser. No. 09/114,505, filed Jul. 13, 1998, now U.S. Pat. No. 5,938,556, entitled "Differential Speed-Sensitive and Torque-sensitive Limited Slip Coupling" discloses a geared differential mechanism with friction clutches for establishing a mechanical torque bias and with a Gerotor pump for establishing a speed-sensitive torque bias. This copending patent application is assigned to the assignee of this invention. The clutches are enclosed in a differential carrier that rotatably supports differential pinions, the pinions engaging coaxially disposed side gears. Each side gear is connected drivably to a separate one of a pair of driven shafts. Torque reaction forces acting on the side gears activate pressure rings which, in turn, energize the clutches. The magnitude of the clutch-engaging force for each of the two clutches is proportional to the torque delivered to the associated driven shaft.
The Gerotor pump has one pump member connected drivably to the differential carrier. A companion pump member is connected drivably to one of the driven shafts. When differential motion between the carrier and the one driven shaft occurs, the pumping elements rotate, one with respect to the other, thereby delivering fluid under pressure through an internal fluid flow circuit with a controlled flow restriction. Fluid is distributed to the Gerotor pump through an inlet port in communication with an external fluid supply, which typically would be located in the axle housing for the vehicle. Upon relative rotation of the pump members, fluid is displaced to a pump outlet port and then recirculated through the pump. The hydrostatic resistance provided by the pump members establishes a speed-sensitive torque bias because the energy applied to the fluid in the closed pump circuit is determined by the relative speeds of the side gear and the differential carrier. The total torque bias for the gear differential mechanism is the sum of the mechanical torque bias and the speed-sensitive torque bias.
The differential carrier is driven by a crown gear or a ring gear, which is drivably engaged with a drive pinion. The combined torque bias provided by the clutches and the Gerotor pump improves the drivability of the vehicle by improving the steering response to a steering effort applied by the vehicle operator and by reducing the possibility of understeering.
The hydrostatic torque bias component of the total torque bias is proportional to the relative speeds of the pump members regardless of the magnitude of the torque being transmitted through the differential.
It is necessary in a differential mechanism of this kind to provide an external fluid source for the Gerotor pump. A relatively large volume of fluid and circulation of fluid through the pump circuit are required in order to ensure that the fluid will not be overheated when the differential mechanism operates continuously for a relatively long period. The necessity for an external fluid supply conduit for the Gerotor pump makes it necessary, furthermore, to increase the size of the differential mechanism and to increase the complexity of the design because of the extended fluid flow path between the pump and the axle housing.